With the advent of plastic pipes and solvent welding techniques the cost of labor in plumbing installations could be significantly decreased. However, the plastic pipes created problems in that they are not adaptable to standard plumbing fittings available for metal pipes. Thus interfacing between metal and plastic plumbing connections required a disproportionate amount of the plumber's time and ingenuity, as did the adaption to plastic pipes of prior art fittings made to fit the conditions of metal pipes.
Furthermore, in the plumbing fitting art, as developed heretofore, different specialty fittings are required for many different functions, making it particularly difficult for the plumber to stock enough different kinds of fittings to meet the problems encountered in the course of his work. For example, one or more different specialty fittings may be required for each of the following listed purposes: clean-out access plug, drain, floor or fabric clamping with and without gaskets, inside pipe mount, outside pipe mount, flush mount, wrench adapter receptacles, cover plates, pipe termial, pipe reduction and enlarging joints, pipe end abutting connection, pipe end non-abutting connection, etc.
Representative of the known prior art pipe end closure fittings are U.S. Pat. Nos. 1,569,875--H. C. Nixon, Jan. 19, 1926 and 3,148,708--P. Panella, Sept. 15, 1964. These provide for fitting metal pipe ends with threaded access caps by means of an intermediate adapter unit compatible with metal pipe. Flush fit on the end of the pipe in Panella is frictionally secured by a rubber O-ring between the fitting and the pipe for engaging the pipe wall frictionally. There is no way to secure this end cap in place to withstand internal pressures or rusted in removable threaded plugs, etc.
U.S. Pat. No. 3,285,289--P. L. Titus, Nov. 15, 1966 provides an adjustable clean-out access fitting for flush mount on a floor and includes a screw-in access plug with an indented wrench receiving socket to avoid floor projections that could cause a person to trip. Flush adjustment is achieved by a series of fittings providing telescopic action by means of screw threads.
Existing plastic pipe fittings commercially available in the art have not been available to withstand considerable pressure and provide leakproof seals for satisfactory use as pipe clean-outs. There are, however, a variety of special purpose fittings for abutting the end of a plastic pipe with dust covers and drain plates mounted thereon, either in solvent welded or snap-in friction fit. These can provide access to internally positioned valves or for clean-out in non-pressurized situations. These substantially constitute a variety of special purpose fittings with plastic cylinders dimensioned for solvent welding or friction fit with a particular dimension plastic pipe. The closure end opening is covered by means of two diametrically spaced screw receiving bosses about the closure end rim for affixing access cover plates or drain plates. In most cases these cylinders have a rather thick flange extending from the cylinder at the closure end serving as a rim about the closure plates.
It is a general objective therefore of this invention to improve the state of this prior art by changing prior art structure to produce a comprehensive universal plastic fitting system for use over a wide range of plumbing problems and which resolves the aforesaid problems of the art. Thus, the plumbing coupling joint assembly of this invention has not heretofore been made available by the art and functions in a mode not heretofore feasible with a single fitting structure.
Other objects, features and advantages of the invention will be found throughout the following description, the drawings and the claims.